The sigma-1 receptor is a ubiquitously expressed unique binding site in the CMS and is a member of the orphan receptor class for which no endogenous ligand is known. Nevertheless, the sigma receptor binds with high affinity to several classes of chemically unrelated ligands such as neurosteroids, neuroleptics, dextrobenzomorphans.and cocaine. Consequently, it is thought that the sigma receptor may mediate the immunosuppressant, antipsychotic, and neuroprotective effects of drugs. Functionally, sigma-1 receptor ligands have been shown to modulate voltage-gated K+ channels independently of G-proteins or kinases. They are also able to mediate calcium release from intracellular stores, regulate compartmentalization of lipids on ER, and have antitumour activity in vitro and in vivo. In terms of structure, there is no available crystal structure of the sigma-1 receptor, but hydropathy analysis suggests there are three hydrophobic regions. Two of these regions have highly conserved residues between the sigma receptor and the yeast C8-C7 sterol isomerase (ERG2), which we believe comprises the binding site. Currently, we aim to probe the binding site region by synthesizing radioactive photoprobes that we hypothesize are interacting with this domain. The Specific Aims for this research are: (1) to pharmacologically and functionally characterize cocaine- and fenpropimorph-derived sigma-1 ligands and photoprobes and (2) to map the Sigma-1 receptor binding site through the use of covalently-bound radiolabeled photoaffinity ligands, proteolysis, and subsequent N- terminal sequencing. The broad objective of this project is to obtain an understanding of the sigma-1 receptor function and structure and its binding site, how it binds various ligands, how it may function as an oligomer, how it functions with ion channels, and what role it may play at a cellular and molecular level. Public Health relevance: Though the exact role of the Sigma-1 receptor has not yet been established, these receptors and their ligands have been implicated in several health-related issues such as modulation of biological actions of cocaine, depression, schizophrenia, cardiac contractility and arrythmias, and regulation of tumor cell growth. These observations are even more significant given that this protein is expressed in several areas of the brain, as well as the adrenal gland, testis, ovary, spleen, and blood leukocytes. Elucidating the structure of the sigma-1 receptor and it's binding site will provide insight as to the functional role of the sigma-1 receptor as well as it's potential as a drug target.